A chemical amplification type positive resist composition is a pattern formation material in which an acid is generated in the exposed area upon irradiation of radiation, for example, a far ultraviolet ray, and solubility in a developing solution between the exposed area and unexposed area is differentiated by a reaction using the acid as a catalyst, whereby a pattern is formed on a substrate.
In case of using a KrF excimer laser as the light source for exposure, since the composition is mainly composed of a resin having as a basic skeleton, poly(hydroxystyrene) that has a small absorption in a region of 248 nm, a good pattern with high sensitivity and high resolution is formed. Thus, the composition is superior to a conventional resist composition of naphthoquinonediazide/novolac resin.
However, when a light source having a shorter wavelength, e.g., an ArF excimer laser (193 nm) is used for exposure, since the aromatic group-containing compound essentially has a large absorption in a region of 193 nm, the above-described chemical amplification resist composition is still insufficient.
The use of poly(meth)acrylate as a polymer having a small absorption in a wavelength region of 193 nm is described in J. Vac. Sci. Technol., B9, 3357 (1991). The polymer has, however, a problem in that resistance to dry etching, which is ordinarily conducted in the semiconductor production process, is low in comparison with conventional phenolic resins having an aromatic group.
In JP-A-2001-192569 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), there is described a mixture of a specific aliphatic sulfonium salt that generates a fluorine-substituted alkanesulfonic acid and a triphenylsulfonium salt or diphenyliodonium salt that generates a fluorine-substituted alkanesulfonic acid, as an acid generator for use in a resist composition.
However, the ArF resist has problems with development defect and PED stability. Therefore, technical developments to solve these problems have been desired.
The term “PED (post exposure delay) stability” as used herein means stability with the lapse of time in that even when a resist is allowed to stand in an exposure apparatus after the exposure until conducting a heating operation, whether a resist pattern having the same linewidth as a resist pattern obtained by conducting the heating operation just after exposure can be reproduced.
The ArF resist has also problems with line edge roughness and profile of trench pattern. The term “line edge roughness” as used herein means a phenomenon wherein an edge between a line pattern of resist and a surface of substrate irregularly fluctuates in the direction vertical to the line due to the characteristics of resist, and when the pattern is observed from just above, the edge is uneven. Since the unevenness is transferred to the substrate in an etching step where the resist is used as a mask, the unevenness causes a defect in electric properties thereby resulting in yield reduction. In particular, the line edge roughness is an extremely important subject to be improved in the field of ultra-fine pattern of not more than 0.25 μm.
Further, in the trench pattern there is a tendency of increasing the line edge roughness as compared with conventional patterns and the improvement therein has been requested.
Also, it is difficult to achieve the formation of rectangular profile in the trench pattern as compared with in the case of line pattern and pent roof-shaped profile is frequently formed by conventional ArF resists. Thus, technical developments to solve these problems have been desired.